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  Image processing method and apparatus, image forming apparatus and system, program and recording mediumUSPTO Application #: 20060103688Title: Image processing method and apparatus, image forming apparatus and system, program and recording medium Abstract: Recording data is produced from first image data corresponding to each pixel with a first number of gradations so as to supplied to a recording apparatus, which expresses each pixel with a number of gradations smaller than the first number of gradations. Second image data is produced by converting the first image data into a color space that can be output by the recording apparatus. Third image data is produced based on a second number of gradations of the second image data so that the third image data has a third number of gradations. The recording data is produced by applying a halftone process to the third image data. The third number of gradations of the third image data is adjusted to be equal to or larger than the second number of gradations of the second image data in accordance with a number of colors for each pixel used in the second image data. (end of abstract) Agent: Cooper & Dunham, LLP - New York, NY, US Inventor: Masanori Hirano USPTO Applicaton #: 20060103688 - Class: 347015000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060103688. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention generally relates to image data processing techniques and, more particularly, to image processing method and apparatus suitable for image forming apparatuses and systems which apply a halftone process to image data. BACKGROUND ART [0002] As a recording apparatus, which prints an image processed by a computer in multicolor and multi-tone (gradation), there is known an inkjet printer (hereinafter, referred to as an IJ printer) which records (forms) an image (also referred to as a dot image) on a recording paper as a recording medium by injecting ink droplets from nozzles provided to a recording head onto the recording paper. Means for generating energy to inject ink droplets in the IJ printer is generally classified into two methods, one being a so-called bubble jet.RTM. method (hereinafter, referred to as a BJ method) and the other being a so-called piezo method (hereinafter, referred to as a PZT type). [0003] The BJ method propels droplets of ink by rapidly heating the ink filled in a pressurizing liquid chamber by utilizing a volume change by film boiling. The PZT method propels droplets of ink by a pressure due to a volume change generated by deforming a diaphragm constituting a part of a pressurizing liquid chamber by displacement of a piezoelectric element. Accordingly, although the pressurization of ink is different between the BJ method and the PZT method, there is no difference in the recording process to form a dot image by injecting ink droplets. [0004] In the meantime, in order to output image data generated by a computer or acquired from an image input apparatus such as a digital camera or a scanner from the IJ printer, various processes must be applied to the image data. Generally, a process flow of image processing is such as shown in FIG. 1. [0005] FIG. 1 is a flowchart of a process of converting input image data into data, which can output by a recording apparatus. In FIG. 1, CMM conversion processes P2 and P6 convert a color system (RGB) of image data P1, which is input as first image data, into a color system (CMY) of an output apparatus such as an IJ printer. BG/UCR processes P3 and P7 separate a black (K) component from the CMY data so as to generate second image data. .gamma.-correction processes P3 and P7 adjust the output balance of each color component separated from the CMY data. Zooming processes P4 and P8 enlarge or reduce the image data so as to match the image data to an output resolution of the IJ printer. Halftone processes P4 and P8 compare each pixel in the enlarged image data with a threshold matrix so as to convert the image data into dot pattern data. An output process P10 outputs the dot image data as third image data. [0006] Usually, image data sent from a personal computer PC has an amount of information with 8 bits for each color RGB per one pixel. Such an amount of information enables expression of 256 gradations from 0 to 255 for each color component. [0007] However, all 256 gradations cannot be used in practice. Since output characteristic of each color component, cyan (C), magenta (M), yellow (Y) and black (K) is dependent on coloring materials used in ink, an injection characteristic of ink droplets and characteristics of recording medium (recording papers), ideal output characteristics cannot be always acquired. Although the .gamma.-correction processes P3 and P7 are applied so as to correct the output characteristics, the .gamma.-correction may cause a lack of gradations mentioned below. [0008] FIGS. 2A through 2F are graphs for explaining a lack of gradations due to a gamma-correction and avoidance of such a lack by an expansion of a gradation level. In FIGS. 2A through 2F, a horizontal axis represents an input tone (input gradation) and a vertical axis represents an output tone (output gradation). FIG. 2D is an enlarged view of a part indicated by a circle in FIG. 2C. FIG. 2F is an enlarged view of a part indicated by a circle in FIG. 2E. FIG. 2A shows a state where no correction is applied and an input and an output correspond to each other on one-to-one basis. On the other hand, since a nonlinear correction as shown in FIG. 2B is usually applied, a lack of gradations as shown in FIG. 2D, which is a partial enlarged view of FIG. 2C, may occur after the correction. [0009] In order to solve such a problem of lacking in gradations, Japanese Laid-Open Patent Applications No. 2001-45308 and No. 2001-285630 suggest a process being performed after enlarging the data input to the CMM process into gradation data of more than 8 bits. Moreover, Japanese Laid-Open Paten Applications No. 2000-108384 and No. 2001-144958 suggest an expansion of a number of gradations with respect to data after the CMM correction. This treatment is to reflect a part, which is eliminated as a value less than a decimal in 8-bit data, as a gradation level. [0010] FIGS. 2C and 2D show the lack of gradations, and FIG. 2E and 2F show an aspect in which the part of lacking gradations (shown in FIGS. 2C and 2D) is not eliminated and is reflected in the corrected data by the expansion of a number of gradations. [0011] Thus, it is possible to avoid an occurrence of lacking gradations due to a gamma-correction by performing an expansion of a gradation level as mentioned above. However, it is natural that an expansion of a gradation level causes an increase in an amount of information. If an amount of information to handle is increased, a capacity of a buffer for operation must be increased. There may be a case where a expansion of a gradation level causes not only a decrease in a processing speed due to an increase in an amount of operation but also a cost increase due to an increase in a buffer capacity. [0012] In recent IJ printers, a number of nozzles mounted on one head unit tends to be increased so as to acquire both a high-resolution and a high-speed operation. Especially, in a BJ printer that is capable of being applied with a photolithography technique, a head having more than 20 nozzles has become popular. Although such an increase in a number of nozzles is to avoid, by increasing the number of nozzles, a problem in that a recording width per a unit number of nozzles is decreased due to a decrease in a nozzle pitch to acquire a high-resolution, an amount of information to be sent to a head at once is increased by an amount corresponding the a number of nozzles increased. [0013] Further, since it is necessary to increase a resolution not only in a sub-scanning direction, which is a direction of adding nozzles, but also in a main scanning direction, an amount of data required for one scan of a head is increased as a square times of the number of nozzles. In association with an increase in an amount of operation in an image processing apparatus due to an increase in resolution, a time lag may be generated between a scan timing of a head and a time of completion of transfer of data to a head unit. In such a case, the operation of the head unit is stopped until necessary data is received, which results in deterioration in effects of the increase in the number of nozzles. DISCLOSURE OF INVENTION [0014] It is a general object of the present invention to provide an improved and useful image processing technique in which the above-mentioned problems are eliminated. [0015] A more specific object of the present invention is to provide an image processing method and apparatus which can reduce a decrease in processing speed while improving reproducibility of gradations by an expansion of a number of gradations. [0016] In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention an image processing method for producing recording data from first image data corresponding to each pixel with a first number of gradations so as to supply the recording data to a recording apparatus, which expresses each pixel with a number of gradations smaller than the first number of gradations, the image processing method comprising: producing second image data by converting the first image data into a color space that can be output by the recording apparatus, the second image data having a second number of gradations; producing third image data based on the second number of gradations of the second image data so that the third image data has a third number of gradations; and producing the recording data by applying a halftone process to the third image data, wherein producing the third image data includes adjusting the third number of gradations of the third image data to be equal to or larger than the second number of gradations of the second image data in accordance with a number of colors for each pixel used in the second image data. [0017] Specifically, the present invention suppresses an unnecessary increase in gradations by adjusting a level of a gradation expansion in accordance with a number of colors used for each pixel in input image data so as to reduce an amount of information to be processed. More specifically, by adjusting a number of gradations so as to be slightly increased or maintained, when producing the third image data, in accordance with a number of colors used for each pixel of the second image data produced, a number of output gradations does not become equal to zero even if a number of gradations of the first image data is a value close to zero. Therefore, a decrease in processing speed is suppressed while improving gradation reproducibility by an expansion of a number of gradations. [0018] In the image processing method according to the present invention, when the second image data is produced using only a primary color that is one of cyan, magenta, yellow and black, when the second image data is produced using a secondary color that is a mixture of only two of the cyan, the magenta, the yellow and the black, and when the second image data is produced using a tertiary color that is a mixture of three of the cyan, the magenta, the yellow and the black, producing the third image data may include adjusting the third number of gradations of the third image data so as to satisfy a relationship"a number of gradations of the primary color.ltoreq.a number of gradations of the secondary color.ltoreq.a number of gradations of the tertiary color". When the primary color is used in the second image data, producing the third image data may not increase the third number of gradations so that the second number of gradations of the second image data is equal to the third number of gradations of the third image data. [0019] In the image processing method according to the present invention, when colors used in the second image data are in a one-color phase system having different brightness, when the colors used in the second image data are in a two-color phase system, and when the colors used in the second image data are in a three-color phase system, producing the third image data may include adjusting the third number of gradations of the third image data by increasing the third number of gradations so as to satisfy a relationship "a number of gradations of a color in the one-color phase system.ltoreq.a number of gradations of a color in the two-color phase system.ltoreq.a number of gradations of a color in the three-color phase system". When the colors in the one-color phase system are used in the second image data, producing the third image data may not increase the third number of gradations so that the second number of gradations of the second image data is equal to the third number of gradations of the third image data. [0020] In the image processing method according to the present invention, producing the third image data may include adjusting a rate of increase in the third number of gradations in accordance with kinds of recording media on which the third image data is recorded. Additionally, producing the third image data may include adjusting a rate of increase in the third number of gradations so that the rate of increase in the third number of gradation when recording is performed on a coated print paper is larger than the rate of increase in the third number of gradations when recording is performed on other print papers including a non-coated print paper and a projector sheet, the coated print paper being applied with a recording agent receiving treatment including a coating treatment on a surface onto which a recording agent including ink and a toner is adhered. [0021] Additionally, there is provided according to another aspect of the present invention a recording medium storing a program for causing a computer to perform an image processing method for producing recording data from first image data corresponding to each pixel with a first number of gradations so as to supply the recording data to a recording apparatus, which expresses each pixel with a number of gradations smaller than the first number of gradations, the image processing method comprising: producing second image data by converting the first image data into a color space that can be output by the recording apparatus, the second image data having a second number of gradations; producing third image data based on the second number of gradations of the second image data so that the third image data has a third number of gradations; and producing the recording data by applying a halftone process to the third image data, wherein producing the third image data includes adjusting the third number of gradations of the third image data to be equal to or larger than the second number of gradations of the second image data in accordance with a number of colors for each pixel used in the second image data. 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